The present invention relates to a method of and circuit for braking an electric drive motor and, more particularly, to a method and circuit for braking a drive motor for driving a grooved drum of a winding head in a bobbin winding machine wherein the motor is braked in a direction opposite to a rated nominal current by loading the motor with a braking current whose strength can be a multiple of the rated current.
In many applications of electric drive motors, attempts are made to brake the motors to a standstill as rapidly as possible. In the case of bobbin winding machines, e.g., in which an electric drive motor drives a grooved drum of a winding head, attempts are made to brake the drive motors as rapidly as possible as required in order to keep the standstill times of the winding heads short and thereby to keep the efficiency of the bobbin winding machine high. Spinning cops are rewound at the winding heads to large-volume cross-wound bobbins. The yarn are monitored during the rewinding for yarn errors. If a yarn error is determined, the rewinding process is interrupted, the yarn piece with the error is cut out, a yarn connection is established between the remaining yarn pieces, and the winding process is restarted. In order to carry this out in as short a time as possible, it is also necessary to bring the grooved drum to a standstill as rapidly as possible.
In order to brake an electric drive motor electrically, it is loaded with a brake current in a direction opposite to the rated current of the motor. The braking time is thereby a function of the magnitude of the braking current, which can be a multiple of the rated current without any concern for damage to the drive motor in the normal instance. Usually, a thermal monitoring device is provided for such drive motors which determines a thermal overload and then interrupts the operation of the drive motor and thereby prevents severe motor damage from occurring as a consequence of overheating of the motor. Such a thermal overloading can occur if a drive motor of a grooved drum is repetitively braked and re-accelerated for short periods of time in succession. The drive motor is then deenergized by the temperature monitoring device and remains deenergized until the temperature has dropped back below the set safety value. As a rule, a red light is also placed at the winding head concerned, which indicates that there is a problem at this winding head which requires an intervention of the operating personnel. This results in standstill times and, in turn, in not insignificant losses of output efficiency of the device or machine involved.